1. Field of the Invention
The present invention relates to a method for controlling a shift of an automatic transmission and a shift control system therefor and, more particularly, to a method for controlling a shift of an automatic transmission of an automotive vehicle and a shift control system therefor, in which plural shift mechanisms to be automatically shifted are disposed sequentially and a shift in such a multistage as forward five speed range positions can be realized.
2. Description of Related Art
Japanese Patent Laid-open Publication (kokai) No. 4,950/1987 discloses an automatic transmission in which two shift mechanisms are disposed sequentially and a shift in a multistage is realized by a combination of a multistage speed range achieved by a first shift mechanism with a multistage speed range achieved by a second shift mechanism. More specifically, if the first shift mechanism would have two forward speed range modes and the second shift mechanism would have three forward shift speed range modes, a combination between the first and second shift mechanisms can realize five forward shift speed range modes. This prior patent publication describes such a method of controlling a shift of the automatic transmission as finishing the shift of the two shift mechanisms at the same time when one of the two shift mechanism is being downshifted while the other is being upshifted, thereby reducing a shift shock due to compensating the deceleration accompanied with the shifting by one of the shift mechanisms for the acceleration accompanied with the shifting by the other thereof.
It can be noted, however, that such an automatic transmission having two shift mechanisms as disclosed in the prior patent publication may amplify changes in a vehicle speed accompanied with a shift to be conducted by each shift mechanism. In other words, when the two shift mechanisms are shifted in one direction. In other words, when both of the shift mechanisms are downshifted or upshifted, the changes in the vehicle speed of the automotive vehicle may be amplified in conjunction with the shift to be made by the two shift mechanisms, thereby making a shift shock larger.